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Ron, It will probably take about 18-20 hours at 250-275*. It's best to cook it by temp and not by time. If you are going to slice it, I would cook it to an it of 180*. If you want to pull it, that goes to 200*. You will have a stall at about 150-160*. When the stall sets in, wrap your shoulder in foil and add a cup of apple juice. The apple juice will add some moisture and a little flavor. The acidity will help with tenderness.
Depends on pit temp and how much each butt weighs. The heaviest one will determine cook time. Weigh each of them, then use the weight of the heaviest one to determine the time. I figure 2 hours per pound when cooking at 250. Keep in mind this just gives a rough time. You really need to cook to temp. Most butts are done when the internal temp reaches 190-205.